Approximately 25% of the 350,000 hip fractures in the US each year occur in men, yet the number of men included in studies of the consequences of this disabling condition has been small. Men who fracture a hip are generally in poorer health than women at the time of a hip fracture and are at almost twice the risk of dying in the year following it. Despite these known differences, surprisingly little information is available about the consequences on hip fractures in men. Because it is not possible to assume that knowledge about hip fracture consequences in women can be applied directly to men who fracture a hip, additional investigation of this understudied group is needed. Before embarking on a large study of this issue in which small effects can be detected, prognostic factors identified, and mechanisms pursued, it is first necessary to demonstrate that there are moderately sized sex differences in key functional, physiological and metabolic changes after a hip fracture. This information can then be used to direct future study and the development of interventions targeted specifically to this group. The proposed study, which is a competing continuation of a Merit Award (R37 AG09901) that has been active for the past 10 years, has two components. Component 1 entails a comparison of 200 male and 200 female hip fracture patients recruited from five hospitals in the Baltimore Metropolitan area on a series of functional, physiologic and metabolic factors that are expected to change following hip fracture. These include bone strength (density, geometry and ultrasound properties), non-bone aspects of body composition (muscle and fat), physical activity and function, psychosocial factors including motivation to recover, and biochemical markers of bone turnover, hormones and the proinflamatory cytokine IL-6. Patients will be recruited for this cohort study during their hospital stay and measured during their hospitalization and again at 2, 6 and 12 months post-fracture. Comparative analyses will be performed. After accounting for attrition due to mortality and other losses to follow up, it is expected that the proposed sample will permit detection of small to moderate-sized (.3 standard deviation) sex differences in study measures. Component 2 of this study has as its goal to determine change in selected aspects of bone, muscle, function, activity, and metabolism attributable to a hip fracture. This aim will be accomplished by comparing the men in the Component 1 cohort with 200 men matched on age and race/ethnicity from an existing study, the Men's Osteoporosis Study (MOST), in which 694 men have been enrolled and are being followed with many of the same measures of interest for Component 1 comparisons. With this new information, the scientific and practice communities will be well positioned to conduct more targeted studies of specific consequences and their mechanisms, and to design and test interventions for optimizing I outcomes after hip fracture in men.